This application relates to catalysts and more particularly to homogeneous catalysts for use in polymerization via the ring opening of strained ring systems, and the polymers formed with such catalysts.
In the presence of Ziegler-Natta catalysts, methylenecyclobutane A can be polymerized into a polymer consisting of a mixture of micro-structure units B and C, through a ring-opening mechanism and a simple vinyl type insertion mechanism, respectively. ##STR1## Micro-structure B is particularly interesting in that it not only represents the thermodynamically unstable form of the synthetic rubberopoly(isoprene), but when incorporated into copolymers with simple olefins, it can impart useful functionalities. Although it has been shown that several Ziegler-Natta catalysts, including AlEt.sub.2 Cl--Cr(acac).sub.3 --TiCl.sub.4 ARA, can selectively produce a polymer with structure B dominating, the activity of these catalysts appears extremely sluggish. More importantly, the mechanism of the ring-opening process which was earlier proposed to involve the oxidative addition of the ring C--C bond seems unlikely with the early transition metals where the required oxidation states may not necessarily be available.